1. Field of the Invention
The present invention relates to an electrophotographic photoconductor, and more particularly to an improved electrophotographic photoconductor comprising an electroconductive substrate, an undercoat layer comprising a binder resin and a modified indium oxide formed on the electroconductive layer, and a photoconductive layer comprising a charge generation layer and a charge transport layer formed on the undercoat layer.
2. Discussion of Background
Recently, there is a tendency for organic photoconductive materials to be widely used as the photoconductors for an electrophotographic copying apparatus because of their advantages of low price, high productivity and non-polluting properties.
As the conventional organic photoconductors, there are known charge-transport type photoconductors, such as polyvinylcarbazole (PVK), and PVK-TNF (2,4,7-trinitrofluorenone), pigment-dispersion type photoconductors such as a phthalocyanine binder, and function-separation type photoconductors in which charge generating materials an charge transport materials are used in combination. Of these photoconductors, the function-separation type photoconductors attract the attention.
When a highly sensitive organic photoconductor of the aforementioned function-separation type is applied to the Carlson process, however, such a photoconductor has several drawbacks. For example, the chargeability of the photoconductor is insufficient for use in practice, and the charge retaining properties is poor so that the dark decay of electric charge is great. In addition, the above-mentioned properties of the photoconductor considerably deteriorate when the photoconductor is repeatedly used. As a result, uneven images with a low image density are produced, and the deposition of toner particles on the background of a transfer sheet readily occurs in the case of reversal development.
In general, the chargeability of a highly sensitive photoconductor is caused to decreases due to pre-exposure fatigue. The degree of the pre-exposure fatigue is mainly affected by the light-absorption of a charge generating material in a photoconductive layer of the organic photoconductor. More specifically, the charge generating material absorbs the light to generate electric charges. The longer these electric charges remain in a movable state in the photoconductive layer of the photoconductor and the greater the number of the above electric charges, the greater the reduction in the chargeability of the photoconductor due to the pre-exposure fatigue. Therefore, even if the photoconductor is charged when the electric charges generated by the light-absorption remain in the photoconductor, the surface electric charge is neutralized by the moving residual charge carriers, so that the surface potential does not increase until the residual electric charges are neutralized and consumed. The rise of the surface potential is delayed by the pre-exposure fatigue, which causes the apparent decrease in the electric potential.
In order to solve the above-mentioned problem, various intermediate layers have been proposed, for instance, intermediate layers comprising a cellulose nitrate resin in Japanese Laid-Open Patent Applications 47-6341, 48-3544 and 48-12034. Intermediate layers comprising a nylon resin in Japanese Laid-Open Patent Applications 48-47344, 52-25638, 58-30757, 58-63945, 58-95351, 58-98739 and 60-6258; intermediate layers comprising a maleic acid resin in Japanese Laid-Open Patent Applications 49-69332 and 52-10138 and intermediate layers comprising a polyvinyl alcohol resin in Japanese Laid-Open Patent Application 58-105155.
In addition to the above, the addition of various electroconductive additives to the resin components in the intermediate layers is proposed to control the electric resistivities of the intermediate layers. For instance, carbon or chalcogen is dispersed in a curing resin of an intermediate layer in Japanese Laid-Open Patent Application 51-65942; a material of an intermediate layer is thermally polymerized by use of a quaternary-ammonium-salt-containing isocyanate type curing agent in Japanese Laid-Open Patent Application 52-82238; a resistivity-controlling-agent is added to a resin of an intermediate layer in Japanese Laid-Open Patent Application 55-1180451; an oxide of aluminum or tin is dispersed in a resin of an intermediate layer in Japanese Laid-Open Patent Application 58-58556; an organometallic compound is added to a resin of an intermediate layer in Japanese Laid-Open Patent Application 58-93062; electroconductive particles are dispersed in a resin of an intermediate layer in Japanese Laid-Open Patent Applications 58-93063, 60-97363 and 60-111255; magnetite is dispersed in a resin of an intermediate layer in Japanese Laid-Open Patent Application 59- 17557; finely-divided particles of TiO.sub.2 and SnO.sub.2 are dispersed in a resin of an intermediate layer in Japanese Laid-Open Patent Applications 59-84257, 59-93453 and 60-32054; and indium oxide is dispersed in a resin of an intermediate layer in Japanese Laid-Open Patent Application 57-81269.
However, the chargeability of the above-mentioned conventional electrophotographic photoconductors gradually decreases while in repeated use. In particular, the rise of the electric potential of the photoconductors becomes insufficient for use in practice and the change in the residual potential is considerable.
The inventors of the present invention have proposed an electrophotographic photoconductor comprising an undercoat layer in which indium oxide is dispersed in a binder resin comprising a reaction product of an active-hydrogen-containing compound and an isocyanate-group-containing compound a in Japanese Patent Application with Application No. 63-61296 (corresponding to U.S. Pat. No. 4,946,766).
The deterioration in the chargeability of the above-mentioned photoconductor is small and the change in the residual potential is slight while in use. However, in order decrease the deterioration in the chargeability and the change in the residual potential, it is necessary to increase the amount ratio of indium oxide to the binder resin. As a result, the dispersibility of indium oxide in the binder resin is lowered, so that the surface of the undercoat layer becomes rough. This brings about the formation of uneven images in the portions which correspond to the rough surface portions of the undercoat layer.